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Petri Nets PN = (P, T, F, M, W)  P : a set of places.  T : a set of transitions that represents the set for tasks, processes, activities, or events.  F : a set of arcs used to represents flow paths   M : an initial marking (M0, ……,Mn)  W : a set of arc weights denoting how many tokens are consumed from a place by a transition

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translate : conceptual services composition ↓ PNML (in XML) Safeness : if it has no more then one token of a Petri Nets Coverability tree algorithm Deadlocked : if no transitions are enabled transitive matrix algorithm Reachable : if it can be generated by a sequence of transition firings beginning at the initial marking